At the center of “Final Solution” are the words of Jewish victims. In mid-August 1942, Rudolf Reder arrived at Belzec on a train that had taken many hours to cover the 60 miles from Lvov. He was assigned to a small group of men held back on the platform, while the rest were led away. “After a few minutes prisoners appeared with stools and hair-cutting equipment: Their job was to shave the women. It was ‘at this moment that they were struck by the terrible truth. It was then that neither the women nor the men — already on their way to the gas — could have any illusions about their fate.’ ” Reder saw how “the women, naked and shaved, were rounded up with whips like cattle to the slaughter, without even being counted — ‘Faster, faster’ — the men were already dying. Two hours was the time it took to prepare for murder and for murder itself.”

The German SS men and the Ukrainian guards “counted 750 people for each gas chamber. Those women who tried to resist were bayoneted until the blood was running. Eventually all the women were forced into the chambers. I heard the doors being shut; I heard shrieks and cries; I heard desperate calls for help in Polish and Yiddish. I heard the bloodcurdling wails of women and the squeals of children, which after a short time became one long, horrifying scream. . . . This went on for 15 minutes. The engine worked for 20 minutes. Afterward there was total silence.” Reder became a gravedigger in the huge burial pits at Belzec and was one of only two inmates known to survive it. Without him, we would know far less about what happened in this first of the Nazi death camps.

It is impossible to read such testimony and not to be overwhelmed by the event itself. There are over 16,000 books devoted to the Holocaust and decades of witness testimony. Among the memoirs and documentaries, exhibitions and — in recent years — the observance of International Holocaust Remembrance Day, a counterculture of skepticism and audience fatigue has grown up. And yet there is something so singular and unimaginable about the events themselves that in this field, unlike many others, historians turn away from metaphor.

As a narrator, David Cesarani, the author of “Becoming Eichmann,” employs a timbre that is clear and somber, the voice of classical realism, as he eschews explicit emotional and moral commentary for the most part, in order not to displace the cumulative impact of his witnesses. Not that Cesarani’s opinions and simmering moral outrage are ever in doubt, as he dispenses with one lingering taboo: Almost every attack and atrocity against Jews was accompanied in Poland, Latvia, Lithuania and Ukraine by rape and sexual violence against Jewish women, sometimes by Germans, sometimes by their local helpers. In Warsaw, well-dressed women were targeted from the start of the occupation, especially those still wearing fur coats. When the mass deportations to Chelmno were underway, many of the Jewish gravediggers were executed at the end of each day’s shift. The Polish ones made themselves so helpful to the SS that they were rewarded by having Jewish women handed over to them. After one or several nights they too were driven into the mobile gas vans and buried in the forest. Male atavism and excess and sexualized violence were everywhere.

“Final Solution” is not an account that will find favor in the new Eastern Europe. Dividing many of his chapters into one slow year at a time, Cesarani achieves a sense of profound claustrophobia by tracing the extreme difficulty of hiding without being caught, blackmailed, denounced and handed over to the Germans in most of occupied Eastern Europe. In Poland, he writes, “village elders, mayors, police officials, firemen, forest rangers and upstanding citizens all took part in Jew-hunts and sought to profit from the mythical wealth of the Jews.” So too did sections of the resistance and partisan movements in Poland and Ukraine. For the approximately 250,000 Jews in Poland who went into hiding, it was the near-hostile environment that made their chances of survival so slim: “Making it through 1943 and into 1944,” Cesarani writes, “was a mountainous challenge.” Robbing Jews continued after their deaths, as people dug into the ash pits of Sobibor and Treblinka looking for valuables that the SS had missed.

Peter Hayes is more circumspect than Cesarani in “Why?,” suggesting that the Poles who actively helped to hide Jews and those who persecuted them were actually both minorities, but that all the institutions of power were stacked on the side of the persecutors. While acknowledging that helping to hide Jews often carried a stigma in postwar Poland, he also points out that over 1,000 Poles were executed by the Germans for doing just that. With his judicious, thoughtful and balanced answers to difficult and often inflammatory questions, Hayes, a professor emeritus at Northwestern, has provided an intellectually searching and wide-ranging study of the Holocaust in a modest, didactic form. He provides just enough thumbnail narrative to frame his very thoughtful answers for a lay audience, as each chapter of the book addresses a particular question — Why the Jews? Why murder? Why didn’t more Jews fight back more often?

Hayes’s answer to this last question is characteristically balanced and astute, as he sketches out the different courses set by four different ghetto leaderships. Whether it was Adam Czerniakow in Warsaw, Chaim Rumkowski kowtowing in Lodz or Jacob Gens in Vilna and Jewish leaders in Minsk who tried to assist Jewish partisan groups, it ultimately made no difference. As Hayes concludes, “whatever the Jewish leaders did — kill themselves, aid the resistance, appease the Nazis — the outcome was the same.” Theirs were truly choiceless choices. Contemporaries may have debated the right course of action, and Cesarani recounts the confrontation between Rabbi David Kahane and Henryk Landsberg, the respected lawyer and head of the Jewish Council in Lvov, in which Kahane declared that “it is better that all die and not one Jew be delivered to the enemy,” while Landsberg countered that the rabbis were not living in the prewar world. But neither Hayes nor Cesarani has any time for the old accusation leveled by Raul Hilberg and Hannah Arendt that without the collusion of the Jewish Councils, the Nazis could not have carried through the Final Solution to the same extent. Cesarani faults the Jewish leaders in Poland not for things over which they had no control, but for their venality and social conservatism when it came to allocating the scant resources they possessed.

Cesarani’s central claim to originality is to reconnect the Final Solution with the military campaigns of World War II. As he argues, recent historiography has shown that “making war” was “the central mission of Hitler and the Third Reich,” but that their preparations for war were “erratic”; that the decisive victories over France, Britain and the Soviet Union in 1940-41 were achieved “mainly thanks to the mistakes of their opponents”; and that the regime’s response to the changing military tide thereafter was marked by “inadequacy.” There are obvious dividends to breaking down the artificial compartments that often separate Holocaust and military historians from one another: It is clear that deporting and murdering the Jews was not allowed to interfere with military priorities. Indeed, one reason the Lodz ghetto was established in December 1939 in a city that had just been formally incorporated as a “German city” within the Reich was that winter coal shortages curtailed all noncritical rail traffic. The same exigency returned two years later, just as the decision to expel all Jews from the Reich and murder them was being communicated to Nazi leaders in Berlin. Again, actual deportation plans were put on hold until the winter crisis on the Eastern front was over.

Recent historians have pointed out how make-do the German war effort was, as industrial capacity was shuttled to solve one bottleneck by creating another. Cesarani applies this insight to the Holocaust. While this interpretation may not be as new as he claims — it was a theme of Gerhard L. Weinberg’s work on World War II — it is well taken, and Cesarani is surely right to insist that “compared to the construction of coastal fortifications in northwest Europe, flak defenses in the Reich or practically any other aspect of the war effort, in material terms the war against the Jews was a sideshow.” It was “low-cost and low-tech.”

What is less clear is what this reading means for how we understand Hitler’s overall aims. Was the Holocaust itself unimportant to Hitler, or was it simply ranked as less urgent compared with the demands of fighting a world war? How does this traditional, Hitler-centric view sit with Cesarani’s insistence that the Holocaust was chaotic and ad hoc, “ill-planned, underfunded and carried through haphazardly at breakneck speed”? Here Cesarani returns to familiar territory, placing the short period of September to December 1941 at the center of the decision-making story. These were months of worsening conditions on the Eastern front as the Germans advanced on Moscow. In this account, Hitler’s final decision about the Jews was made at the time he declared war on the United States, on Dec. 11. The murder of the Jews may have been a second-order objective to winning the war, but in the end that fact tells us more about practical reasoning and immediate priorities than it does about core aims.

For Cesarani no less than for Saul Friedländer or Ian Kershaw, Hitler’s obsessive hatred was still the driving force. And on the final page of this magnificent book, he returns to Hitler’s political testament to show that he remained consistent in blaming the Jews for Germany’s defeat in 1918. Behind the chaos, he once more reveals a central will to destroy.

Both Hayes and Cesarani reinstate the singularly Jewish character of the tragedy. The murder of the Roma and disabled is sidelined: Cesarani is too good a historian to omit this from his narrative, but these victims remain voiceless, with no witness testimony cited. Indeed, Cesarani insists that it was the firing squads in Poland and not the gassing of psychiatric patients in Germany that “created the model for mass murder.” Undoubtedly, in Nazi minds the Jews were an all-powerful international enemy, the focus of both fear and hatred, which marked them out as a different kind of enemy from Roma, the disabled or Soviet civilians. But if one’s aim is to reconnect genocide with the rest of the German war, then these other victims also deserve to be written into the story.

Both of these books are the culmination of careers devoted to explaining the Holocaust. In his retirement, Hayes has given us “Why?” as his last lecture course. Cesarani finally wrote the book he had turned away from writing 15 years earlier. His own unexpected death while it was in preparation means that this indefatigable contributor to public debate in Britain could neither enjoy nor participate in the reception of his magnum opus. We are in his debt.

Nicholas Stargardt is a professor of modern European history at the University of Oxford. His most recent book is “The German War: A Nation Under Arms, 1939-45.”